1. Field of the Invention
The present invention relates to a substrate cross-section observing apparatus, and more specifically to an apparatus for observing a microminiature cross section of a semiconductor substrate such as a wafer (on which a micro-miniaturized pattern is formed) with the use of a charged beam.
2. Description of the Prior Art
When a cross section of a wafer on which a micro-miniaturized pattern is formed is required to be observed, the wafer is cut off by use of a diamond cutter, for instance and then the wafer is broken off along the scar to expose the cross section, so that the worker can observe the exposed cross section of the wafer. Further, after the exposed observation cross section has been processed so as to be suitable for electron microscope observation, the processed observation cross section of the wafer is to be observed.
In the conventional method of forming the observation cross section, the microminiaturized pattern portion to be observed is first selected by visual inspection or work and then must be cut off along the selected cross section by use of the diamond cutter. Or else, the microminiaturized pattern portion to be observed is cut off by use of the diamond cutter, without any selection, so that the cut off surface may pass through a great number of the microminiaturized patterns. Accordingly, a great deal of skill has been so far required for the work for forming the observation cross section. In addition, where the observed pattern is separated alone or where the observation positions have been already determined, it is extremely difficult or rather impossible to accurately cut off the determined observation positions by use of a diamond cutter.
To overcome these problems, various apparatus of observing wafer cross sections have been so far developed. As one of the examples of these wafer cross section observing apparatus, there exists such an apparatus that: any required microminiaturized pattern portion is irradiated with an etching ion beam to form a bore of about several .mu.m in the vertical direction in the surface of the wafer, and the vertical wall surface of this formed vertical bore is irradiated with an observing ion or electron beam obliquely from above for electron microscope observation.
In the above-mentioned prior art wafer cross section observing apparatus, however, since the observing ion or electron beam is irradiated upon the observation cross section obliquely from above, there exists such a problem in that it is impossible to check the vertical dimension of the observation cross section intuitively.
To overcome this problem, there exists such a method of increasing the diameter of the bore for observation and further of irradiating the observing ion or electron beam upon the observation cross section roughly in the vertical direction. In this method, however, since a long etching time is required to form a large diameter bore for observation, which raises another problem in that the observing efficiency is inevitably lowered.